Natural plant and microorganism-based oils possess excellent potential for health benefits through ingestion. For example, beneficial health effects of consuming polyunsaturated fatty acids (PUFAs), which include eicosapentaenoic acid (C20:5, ω3) (EPA), docosahexaenoic acid (C22:6, ω3) (DHA), and arachidonic acid (C20:4 ω-6) (ARA), have been well documented for many years. These fatty acids have been linked to visual and mental health as well as regulation of critical biological functions. PUFAs are associated with the prevention and treatment of coronary heart disease and abnormal cholesterol levels, in addition to alleviating inflammatory conditions and even retarding growth of tumor cells. PUFAs are also precursors to a variety of metabolites, including prostaglandins and leukotrienes that regulate critical biological functions.
High ratios of ω-6 to ω-3 PUFAs typical of the Western diet (e.g., 15:1-17:1) have been linked to common maladies like heart disease, cancer and other metabolic disorders. Lowering this ratio is considered to be essential for lowering the risk of many chronic diseases. Accordingly, it is generally held that the ω-6: ω-3 ratio should be taken into consideration when producing a supplement. For instance, U.S. Pat. No. 5,550,156 to Kyle discloses a 2:1 blending of ARA and DHA for supplementing infant formula for the purpose of increasing the PUFA amounts and ratios to simulate the natural blend found in human breast milk.
Fish oil supplements dominate the current PUFA-rich oil market. Unfortunately, however, fish oil can possess objectionable tastes and odors and may contain cholesterol as well as pollutants such as mercury. Microorganisms as well as agricultural sources are promising producers of PUFA-rich oils that can serve as an alternative to fish oils. For instance, microorganisms including algal and fungal sources are capable of year-round oil production on a variety of cheap substrates. For example, the fungi Pythium irregulare is capable of high production of intracellular oil containing the PUFAs EPA and ARA as well as other long chain fatty acids such as linoleic acid (C18:2, ω-6). Submerged culture studies investigating oil production over a broad temperature range (14° C., 21° C., and 28° C.) have found maximum oil production, 0.893 mg/ml, occurring at 21° C. and 4 days of fermentation. Commercially feasible technology to produce EPA and DHA from microalgae and fungi is being investigated on many fronts.
Plant and microorganism-based oils are also becoming attractive as replacements for non-renewable petroleum. For instance, algae are the highest yield feedstock found to date for production of oils as may be utilized in formation of biodiesel, lubricants, and the like. Biodiesel, a biodegradable, non-toxic fuel formed from transesterification of any of a variety of vegetable oils or animal fats, has long been considered a viable option to petroleum-based diesel (petrodiesel). Biodiesel can be utilized as formed in unmodified diesel engine vehicles and furnaces, can be easily blended with petrodiesel, and typically produces about 60% less net carbon dioxide emissions than petrodiesel. It is estimated that between 250 and 300 billion gallons of diesel oil is used annually in the United States for transportation fuels and home heating oil. Of this amount, only about 8% comes from renewable resources. Moreover, while relatively few automobiles in the U.S. utilize diesel fuel, the opposite trend exists in Europe, with total diesel consumption in the U.S. from trucks, buses and other transportation estimated to be about 80% of Europe's consumption level.
Between 1978 and 1996, the U.S. National Renewable Energy Laboratory (NREL) examined the possibility of using algae as a biodiesel source. These studies resulted in a collection of approximately 300 different species of algae, both fresh-water and salt-water, and made them available to researchers from around the world. This initial work on algal biodiesel development was curtailed in the mid-90's, due primarily to a drop in crude oil prices and government budget cuts. Interest in biodiesel from algal oils has revived due to both increasing crude oil prices and increasing interest in energy independence from fossil fuels.
Unfortunately, problems exist with conventional methods utilized for oil recovery from biomass. These conventional methods include organic solvent extraction, vacuum distillation, and maceration, all of which can present ecological problems both during production and with regard to waste disposal. Other problems concern product recovery, as natural oils such as PUFAs are susceptible to thermal and oxidative degradation under the harsh conditions these techniques employ. In addition, oils for human consumption should be obtained using methods that employ solvents that are acceptable in terms of toxicity, handling, safety and cost.
What is needed in the art are improved methods for obtaining high value lipids from biomass.